Your donor vehicle is ALSO a 4WD...right?
Conversion U-joint generally a Precision 447 or equivalent.
Four U-bolts + nuts, big enough to fit the larger axle.
The larger U-bolt mounting plates for the "new" axle--take 'em from the donor vehicle.
Rear cover gasket 'cause you're gonna pull the cover to inspect the gears 'n' bearings in the replacement axle
Gear lube suitable for the replacement axle
Maybe axle seals and/or pinion seal--are they leaking?
Whatever rear brake parts are needed for safe and effective rear braking. (Shoes? Hardware/springs/adjusters? Wheel cylinders? Drums?)
Brake fluid for flushing the brake hydraulic system.
Re-use everything else that's in good condition. The existing park brake cables will connect to the (hopefully) larger rear brakes--assuming the existing cables haven't seized from non-use. Excellent time to replace the rear shocks, rear brake hose/brake tubing, and to verify the leaf springs/spring bushings.
Driveshaft shoves into the transmission or transfer case an extra half-inch or so--so clean 'n' polish the driveshaft slip-yoke.
